This application is based on Patent Application No. 2001-246240 filed Aug. 14, 2001 in Japan, the content of which is incorporated hereinto by reference
1. Field of the Invention
The present invention relates to a sub-tank of an inkjet printing head and, more particularly, to an inkjet printing head having a mechanism for discharging gases that have entered and accumulated in the sub-tank.
2. Description of the Related Art
In an enclosed type liquid container, gases that have been dissolved in a liquid in the container and gases that have passed through members of the container from outside are accumulated with the passage of time. An increase in the quantity of gases in the liquid container cancels a negative pressure required for holding the liquid in the container. Especially, in the case of an inkjet printing head having such an enclosed type light container, this disables proper ejection of the liquid and results in leakage of the liquid from the nozzle.
A countermeasure to this problem is to minimize gases trapped in the liquid container by employing materials having low gas permeability as materials of members used for the container, but it is still insufficient to eliminate the accumulated gases completely.
Referring to inkjet cartridges that are one type of liquid containers in the related art, such cartridges are frequently replaced when liquids in the liquid containers have run out, and the above problem has been avoided by replacing the cartridges in most cases. In such cases, however, the cartridges must be thrown away with liquids left in the containers, which undesirably results in the waste of containers and liquids. In the case of inkjet cartridges that are used with liquids repeatedly being charged, the above-described situation remains and there is no solution to this problem at all.
Another possible countermeasure to the problem is to discharge the accumulated gases to the outside periodically. However, when this is attempted by taking advantage of a recovery operation in the related art for sucking a liquid from a nozzle, the accumulated gases cannot be discharged efficiently because a liquid in the container is also discharged, and only the gases may finally remain in the container.
A possible measure to avoid this is to form a channel for communication with outside separately from an ink channel to a nozzle. A discharge port provided at the bottom of a liquid container sufficiently works as a channel for charging a liquid. However, when the accumulated gases are discharged, the liquid is discharged first, leaving the accumulated gases without discharging the gases as in the case of the recovery operation in the related art. Even if a chimney-like configuration is employed in which the opening of the channel is located at the top of the container, a consuming efficiency of a liquid can be decreased in the case of a container having a movable section constituted by a sheet, for example, because the chimney can impair the movability of the sheet depending on the position where the chimney is formed.
The present invention confronts the above problems and provides an inkjet printing head having a liquid container from which the accumulated gases can be easily discharged.
According to the present invention this is achieved in an inkjet printing head, characterized in that it has a movable section constituted by a deformable film sheet, a spring for imparting a negative pressure, and a sub-tank having a supply/discharge channel for supplying ink and discharging accumulated gases, the sub-tank being intermittently supplied with ink from a main tank and reserving the ink, and in that the supply/discharge channel is provided in a position where it does not interfere with the movable section and the spring.
The sub-tank may have a frame, and the supply/discharge channel may be formed in the frame.
An opening of the supply/discharge channel is preferably formed in an upper part of the sub-tank, and the opening may be formed at a ceiling section of the sub-tank.
The ceiling section of the sub-tank may be inclined toward the opening of the supply/discharge channel.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.